“What’s the point if having ‘door open’ buttons on the outside of MAX trains? It seems like every time a child gets separated from an adult at a station, there’s a surveillance video of someone desperately trying to get the train’s doors to open by pushing those buttons. They never work.”

What we have here is a basic misunderstanding of coming and going.

Of course, TriMet hasn’t done a bang-up job of educating the public about when we can and can’t use those buttons. Basically, they’re designed to work when MAX is coming. Or, more precisely, when it has arrived.

That buttons are for the rare times when an in-service light rail train pulls into a station and its sliding doors don’t deploy. Hit the button and they should hiss open like they’re on the Starship Enterprise -- as long as the operator has set them for release.

Last week, TriMet released video of an aunt getting separated from her nephew as they ran to catch a train at a downtown stop.

The boy pulled away from the woman and dashed onto the train just as the doors closed. She started hitting the “door open” button, only to watch the train pull away. Fortunately, they were reunited a few blocks away.

Once an operator closes a train’s doors for departure, they are locked into place (no one wants doors flying open as the train starts moving, right?).

So what’s the trick to getting a train’s closing doors to reopen? Well, you could let them close and wait for the next train. Or, said TriMet spokeswoman Mary Fetsch, “Touch the sensitive edge of the door.”

The sensitive what now?

“We can’t go too much into how it works,” she said, “because we don’t want to encourage vandalism.”

Apparently, the sliding train doors operate a lot like elevator doors, with rubber bumpers that sense when someone touches or just thrusts a hand into the opening to stop them from shutting.

“So,” I asked Fetsch, “you’re telling me that if I stick my hand into a closing MAX door, it won’t close on me and the train won’t drag me away.”